The present invention relates to the supplying of gas, such as a gaseous mixture based on diborane (B.sub.2 H.sub.6) and of silane (SiH.sub.4), destined for a reactor for growing layers of glass having a base of boron, phosphate, silicate (BPSG) ("boro-phospho-silicate glass) beginning with an initial feed of B.sub.2 H.sub.6/ SiH.sub.4 in determined proportions.
It is known that this type of mixture is modified with time by virtue of the tendency of diborane (B.sub.2 H.sub.6) to be transformed to higher boranes, notably those such as tetraborane (B.sub.4 H.sub.10), pentaborane 11 (B.sub.5 H.sub.11) which, on one hand, release hydrogen (H.sub.2) and, on the other hand, are sometimes transformed to a liquid or even solid form which is not transferred with the gaseous flow. As a result, even when starting from perfectly suitable starting materials, the mixture transferred to the reactor is of improper composition notably, the mixture being of lower boron content, which forestalls against proper growing of the BPSG glass layer. This is the reason that, currently, analyses of the gaseous mixture being transferred to the reactor are carried out such as by chromatography which is not very practical because such method is discontinuous and requires frequent recalibration.